1. Field of the Invention
This invention relates to a method for checking the noise performance of spectrometers and spectrophotometers.
2. Description of the Prior Art
Frings et al. (1) report that the percentage of quantitative analyses performed in the clinical laboratory that involve spectrophotometry or colorimetry was estimated in 1969 to be possibly more than 95% (2). Most laboratories continue to rely heavily upon spectrometers or spectrophotometers for the majority of their analyses. Maintenance of properly functioning spectrometer and spectrophotometers is an obvious prerequisite to the assurance of accurate analytical results. Moreover, the increased regulation of clinical laboratory by governmental and professional agencies mandates that laboratory personnel periodically verify that a given spectrophotometer is functioning properly. By periodically inspecting spectrometric and spectrophotometric functions, subtle or gradual degradations in performance can be detected before they significantly affect analytical results. As a minimum, these inspections should include, inter alia, a check of noise, i.e., the random variation of signal with time.
To measure noise, one measures the absorbance (A) or percent transmittance (%T) of a solution having a broad absorption band and a maximum absorbance of about 2.0 A over a period of time.
One prior art solution employed in the past to measure noise is a potassium dichromatic solution (0.05 gm/l). This solution has an absorbance of about 2.0 A at 372 nn.
The potassium dichromatic solution possesses a relatively short shelf life, i.e., it has been observed to decrease in absorbance at a rate of about 0.02 A per month.
Accordingly, it would be very desirable to have a noise check solution which possesses all the desirable properties of the dichromatic solution and also possesses a very stable shelf life.